The present invention relates to a process for the manufacture of vaccines for immunizing egg-laying birds, particularly chickens, against a disease (referred to herein as "Egg Drop disease") caused by a novel virus which adversely affects egg production and quality, to the vaccines so produced from the novel virus, and to the use of the vaccines.
Egg production is known to be adversely affected by a number of different factors, for example, poor food. A drop off in egg production sometimes is a side-effect of viral infections causing other diseases, e.g., those affecting the respiratory tract caused, for example, by an infection with Newcastle Disease Virus. An infection in chickens caused by Egg Drop disease virus was so far unknown or at least not widespread as appeared from the results of an examination of sera taken between 1973 and 1974 from 12 flocks which showed that none had antibodies to this virus. Recently, however, this particular type of Egg Drop disease has been observed in a number of countries. One of the features of this disease is that the shell gland may be affected, and egg production is depressed. Antibodies to this virus have been detected in 20 to 24 flocks of ducks sampled and the virus would appear to occur naturally in this species.
The casual organism of this disease appears to be a novel type of virus apparently unrelated to other known avian viruses, except insofar as certain minor proteins and morphological characteristics may be shared by avian adenoviruses.